The present invention relates to train/locomotive location systems and, more particularly, to train location systems for continuously and accurately identifying the location of a train on or within a trackway system using a train-mounted navigator geo-positional receiver solution in combination with track database information. Various systems have been developed to track the movement of and location of railway locomotives/trains on track systems including the system disclosed in U.S. Pat. No. 6,641,090 to Thomas J. Meyer and the system disclosed in commonly assigned U.S. patent application Ser. No. 10/980,191 filed Nov. 4, 2004 by Thomas J. Meyer (the respective disclosures of which is incorporated herein by reference); in these location determination systems inertially sensed orthogonal acceleration inputs and turn-rate information and GPS/DGPS information are combined with other inputs, such as those provided by one or more wheel-mounted tachometers, to provide information related to velocity and location.
Typically, track databases are maintained that store track information including the absolute and relative position of tracks and track transitions such as, for example, switches, turnouts and crossovers. Ideally, railroad tracks are perfectly uniform and remain consistent with their original design as straight sections connected by constant curve and spiral sections. In practice, however, weather and geographical conditions, train speeds, tonnage, and continued maintenance requirements contribute to railroad track non-uniformities. The Federal Track Safety Standards (FTSS) divides railroad track into nine (9) speed-related classifications as a function of speed (49 C.F.R. 213) with permissible variations of track geometry provided for each track class as shown, for example, in the following table for tangent track classes 1-5:
Tangent TrackThe deviation of the mid-chord off-set from a 62 ftline may not be more thanClass of Track(inches)Class 1 Track5Class 2 Track3Class 3 Track1¾Class 4 Track1½Class 5 Track ¾
In the table above and as shown in FIG. 1, the alignment deviation (viz., side-to-side or lateral deviation) for straight tangent tracks is defined as the mid-offset deviation from a 62 foot chord line. As shown in the table above, the deviation varies from a maximum of 5 inches for a class 1 track to 0.75 inches for a class 5 track with analogous dimensional limits specified for curved track. In addition to the alignment deviations shown in FIG. 1, standards also exist for profile deviations (i.e., change along the up/down axis for a chord of a selected length). Although the FRA (Federal Rail Administration) regulates the amount of track irregularities permitted for each track class (Class 1-9), most track database information carries errors that can change with time and which are often difficult to and expensive to ascertain with accuracy.
Track databases can be created from the original design specification for the straight tangent sections, the curved sections, and the spiral track sections, although inconsistencies can exist between the tracks as designed and the tracks as initially built, and the tracks after years of use. Track databases can also be created from physical surveys of the tracks, although highly accurate surveys are considered costly.
Additionally, databases can be assembled from information based upon the track as surveyed and the track as designed using data “fitting” techniques intended to increase the probability that the so-assembled database will more closely approximate the actual track.
As shown in FIG. 2, side-to-side alignment deviations can affect heading inputs and path length inputs. In FIG. 2, points A and B represent endpoints through which the physical track (dotted-line) passes; in the as-designed database, the path length between points A and B is shown as a straight solid line. For a locomotive traveling from the left at a constant velocity and passing though point A toward point B, expected heading inputs and acceleration inputs should be relatively constant. As shown by the non-straight physical track path (dotted-line) caused by track deviations, the actual heading inputs will vary about the nominal database heading, any acceleration inputs expected between the A-B points will varying as a consequence of the side-to-side deviations, and the actual path length between points A and B will be greater than the database value because of the side-to-side deviations. The more general case is shown in FIG. 3, in which actual track path (dotted-line) continuously deviates from one side to the other with corresponding changes in heading; the measured inputs from the perspective of the locomotive will show substantial variation in heading, acceleration values, and distance traveled that will be different from the database model which will expect substantially less heading, acceleration, and distance traveled variation/values.
Accurate track databases are desired to reduce the probability of false wrong-track alarms, i.e., those situations in which the position information obtained from on-board navigation equipment of the type disclosed in the above-incorporated patent and patent application deviates from the database information sufficiently to raise a position-error alarm or a track-error alarm. In those cases where the accuracy of the a priori database is known to be poor, the fault detection system(s) are operated with ‘loose’ fault-tripping criteria to minimize the number of false alarms and minimize those fault alarms triggered by inaccurate data predicted by the database. As can be appreciated, a need exists to treat or condition measured navigation inputs in such a way to address the errors introduced by track class-constrained track irregularities in order to effect simultaneous navigation and track database compensation.